Learn the differences between different types of targets

[github-learning-lab]

remake is the R package that underlies many of scipiper's functions. Here we've borrowed some text from the remake github repo (credit to richfitz, although we've lightly edited the original text) to explain differences between targets

Targets

"Targets" are the main things that remake interacts with. They represent things that are made (they're also the vertices of the dependency graph). If you want to make a plot called plot.pdf, then that's a target. If you depend on a dataset called data.csv, that's a target (even if it already exists).

There are several types of targets:

• files: The name of a file target is the same as its path. Something is actually stored in the file, and it's possible for the file contents to be modified outside of remake (files are the main types of targets that make deals with, since it is language agnostic). Within files, there are two sub-types:
  • implicit: these are file targets that are depended on somewhere in your process, but for which no rule to build them exists (i.e., there is no command in a remakefile). You can't build these of course. However, remake will build an implicit file target for them so it can internally monitor changes to that file.
  • explicit: these are the file targets that are built by rules that were defined within your pipeline (i.e., command-to-target recipe exists in a remakefile).
• objects: These are R objects that represent intermediate objects in an analysis. However, these objects are transparently stored to disk so that they persist across R sesssions. Unlike actual R objects though they won't appear in your workspace and a little extra work is required to get at them.
• fake: Fake targets are simply pointers to other targets (in make these are "phoney" targets). The all depends on all the "end points" of your analysis is a "fake" target. Running scmake("all") will build all of your targets, or verify that they are up to date.

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